Vertical type pulverizing and classifying apparatus

Abstract

The invention provides an improved vertical type pulverizing and classifying apparatus comprising a lower, pulverizing chamber and an upper, classifying chamber, wherein a material under treatment is carried by gas streams. The disclosed apparatus includes a conduit between the pulverizing chamber and the classifying chamber for sending particles of the material emerging from a primary classification to the classifying chamber for a secondary classification. A floating chamber is provided circumferentially of the conduit to receive particles descending from the classifying chamber for a further classification, whereby resulting fine particles are blown back to the classifying chamber and coarse particles are returned to the pulverizing chamber by way of a material feeder.

We claim: 
     
       1. A vertical type pulverizing and classifying apparatus comprising: a pulverizing chamber provided with a pulverizing rotor disposed within a housing having upper, medial and lower portions,   a guide ring stationarily disposed above and coaxially with the pulverizing rotor, the guide ring defining inwardly thereof a descending gas stream passage for primary classification of material pulverized in the pulverizing chamber,   a classifying blade rotor disposed above and coaxially with the guide ring and driven so as to rotate within an upper housing portion, the blade rotor and the upper housing portion serving to define a classifying chamber therebetween for secondary classification of material fed from the guide ring,   a collecting passage disposed above the blade rotor into which fine particles from the classifying chamber flow is fed by gas streams,   a first material carrying gas feed duct disposed below the pulverizing rotor,   a plate member provided with pores disposed between the descending gas stream passage and the classifying chamber and arranged to serve as a partition therebetween,   a conduit having extremities axially disposed such that one extremity terminates within a zone defined by the guide ring and the opposite extremity extends through the plate member so as to terminate within the classifying chamber,   a second gas feed duct disposed below the plate member and arranged to supply a flow of gas to the pores of said plate member,   a coarse material floating chamber disposed within said medial housing portion above the plate member, said chamber being defined by said medial housing portion and the upper extremity of the conduit, and   return passage means disposed exteriorly of said housing and extending from coarse material floating chamber to said lower housing portion and into said pulverizing chamber, whereby coarser particles are separated from finer particles and recylced for further pulverizing.   
     
     
       2. An apparatus as claimed in claim 1, further wherein said return passage means comprises a transfer duct connected to a material feeder, the coarser particles being fed from the coarse material floating chamber to the pulverizing chamber thereby. 
     
     
       3. An apparatus as claimed in claim 1 characterized in that the plate member (16) is in a frustoconical form defining the pores (16a) only in a periphery of a conical part thereof disposed downwardly. 
     
     
       4. An apparatus as claimed in claim 3, further wherein said return passage means comprises a transfer duct connected to a material feeder, the coarser particles being fed from the coarse material floating chamber to the pulverizing chamber, thereby. 
     
     
       5. An apparatus as claimed in claim 3 characterized in that an entirety of the frustoconical plate member (16) is inclined toward an inlet opening of the transfer duct (18). 
     
     
       6. An apparatus as claimed in claim 5, further wherein said return passage means comprises a transfer duct connected to a material feeder, the coarser particles being fed from the coarse material floating chamber to the pulverizing chamber thereby.